CHARLOTTE, N.C. — The hospital in Liberia where three U.S. aid workers got sick with Ebola has been overwhelmed by a surge in patients and doesn’t have enough hazard suits and other supplies to keep doctors and nurses safe, a missionary couple said Wednesday.

The latest infection — Rick Sacra, a doctor who wasn’t even working in the hospital’s Ebola unit — shows just how critical protective gear is to containing the epidemic, and how charities alone can’t handle the response, they said.

Nancy Writebol and her husband, David, called for reinforcements during the interview, which followed her first news conference since recovering from Ebola disease. They work for North Carolina-based SIM, the charity that supports the ELWA hospital in Monrovia, Liberia.

About 250 employees at the hospital use thousands of disposable protective suits each week, but that’s not enough to fully protect the doctors and nurses who must screen people entering the emergency room or treat patients outside the 50-bed Ebola isolation unit, they said.

“We don’t have enough personal protective-safety equipment to adequately be able to safely diagnose if a patient has Ebola. So they are putting themselves at risk,” David Writebol said.

Sacra, 51, a doctor from suburban Boston who spent 15 years working at the hospital, felt compelled to return despite these challenges. As soon as he heard that Dr. Kent Brantly and Nancy Writebol were sick, Sacra called and said: “I’m ready to go,” SIM President Bruce Johnson said.

Sacra’s job was to deliver babies and care for patients who were not infected with Ebola. He helped write the protocols for handling Ebola, his brother Doug said, and he followed all the protections, said Will Elthick, the group’s operations director in Liberia.

But he got infected nonetheless by the virus that has killed more than 1,900 people and sickened 3,500 in five West African nations. Discovered in 1976, Ebola is an aggressive virus that causes high fevers, extreme weakness and internal bleeding, with a fatality rate as high as 90 percent.

The disease is spreading faster than the response to it because of the lack of protective gear and caregivers, said Tom Kenyon of the U.S. Centers for Disease Control and Prevention (CDC). At least $600 million is urgently needed to provide these tools and extra hazard pay so that more doctors and nurses are willing to risk their lives, the World Health Organization (WHO) said Wednesday.

Health-care workers at other West African hospitals have gone on strike demanding more protections, the Writebols said. “They see colleagues who have fallen. They don’t want that to happen to them,” David Writebol said.

The Writebols left Charlotte for Africa several years ago; David helped with the hospital’s technology while Nancy helped dress and disinfect people entering and leaving the Ebola unit at ELWA, which stands for Eternal Love Winning Africa.

Liberians were already struggling to survive when they got there, but with Ebola it’s chaos: The number of patients is surging, finding food and supplies is more costly, schools are closed and people with common injuries or even mothers in childbirth can’t get care.

Sacra immediately got tested for Ebola after coming down with a temperature, and like his colleagues, went into isolation to avoid spreading the virus, his brother Doug Sacra said.

Some other doctors haven’t been so rigorous. WHO said Wednesday that a doctor in southern Nigeria was exposed by a man who evaded surveillance efforts.

The doctor in turn exposed dozens of others by continuing to treat patients after he became ill. Now his widow, also a doctor, and sister are sick and about 60 others in the city of Port Harcourt are under surveillance, the agency said.

Sacra, meanwhile, was in good spirits Wednesday and able to send emails. It’s not clear where he would be treated in the U.S. There are four high-level isolation units designed especially to handle dreaded infectious diseases. The largest is at the Nebraska Medical Center in Omaha. The other three units are National Institutes of Health facilities in Maryland and Montana and Emory University Hospital in Atlanta.